Influence of heat input on high temperature weldment corrosion in submerged arc welded power plant carbon steel

This paper describes an experimental work carried out to evaluate and compare corrosion and its inhibition in SA 516 Gr.70 carbon steel boiler weldments made by submerged arc welding process with four different heat inputs exposed to hydrochloric acid medium at 0.1 M , 0.5 M and 1.0 M concentrations. The parent metal, weld metal and heat affected zone are chosen as regions of exposure for the study carried out at 100 °C. Electrochemical polarization techniques such as Tafel line extrapolation and linear polarization resistance have been used to measure the corrosion current. The role of hexamine and mixed inhibitor (thiourea + hexamine in 0.5 M HCl), each at 100 ppm concentration is studied in these experiments. Microstructural examination, surface characterization using scanning electron microscopy and X-ray diffraction have also been made on samples in order to highlight the nature and extent of film formation.